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income and employment theory, a body of economic analysis concerned with the relative levels of output, employment, and prices in an economy. By defining the interrelation of these macroeconomic factors, governments try to create policies that contribute to economic stability.

Modern interest in income and employment theory was triggered by the severity of the Great Depression of the 1930s in the United States and Europe. In its failure to explain the persistent high levels of unemployment and the low levels of business productivity, the prevailing school of classical economics lacked solutions for the problems of that era.

John Maynard Keynes offered new thinking on income and employment theory with the publication of General Theory of Employment, Interest and Money (1936). Building on his theory, Keynesians have stressed the relationship between income, output, and expenditure. Since transactions are two-sided—in that one person’s income is another person’s expenditure—the relationship could be expressed in the form of a simple equation: Y = O = D, where Y is the national income (i.e., purchasing power), O is the value of the national output, and D is national expenditure. What this equation means is that effective demand is equal to income as well as to output. Since consumers can either spend or save their income, Y = C + S, where C is consumption and S is savings.

Similarly, on the output side, production is either sold to final customers or invested in inventory or new capital equipment, (such as production plants or machinery). So O = C + I, where C represents sales to final customers and I investment. Thus, C + S = C + I and, therefore, S = I. However, while savings and investment may thus be equated from an accounting standpoint, in fact, actual planned savings and planned investment may differ in real life. Keynesians say that economic instability stems from this discrepancy between savings and investment.

Suppose, for example, that in a given period savings rise above their previous levels. The effect will be a reduction in present demand with a prospect of increased future demand. If, by coincidence, additional capital formation (investment, such as in inventory) rises by the same amount, productive resources will continue to operate at capacity; there will be no change in the level of activity, and the economy will remain in equilibrium. However, if capital formation does not rise, then the demand for labour will fall and, assuming that wages do not fall, some workers will become unemployed and lose some of their current income.

The fall in incomes further reduces consumer demand while also reducing the rate of savings. Provided manufacturers do not alter their investment plans, equilibrium will be established at a lower level of income. In reality, then, it is not savings that are unstable but the level of investment: a fall in investment and an increase in savings will both produce a dampening effect on the economy. Conversely, a rise in investment or an increase in consumer spending will tend to stimulate the economy.

This example illustrates how changes in savings or investment will affect changes in national income, but it does not show the extent of those changes. The actual degree of change is determined by what Keynes called the “consumption function” (that is, the level of spending that is based on disposable income). Keynes’s primary aim in developing his theory was to show that, under certain conditions the economy could become stuck in a disequilibrium, with productive resources in surplus (i.e., high level of unemployment) but income and output unable to rise sufficiently to reach an equilibrium. Put simply, Keynes argued that, when business was unwilling or unable to increase investment because of low demand, additional government spending could spur new spending and eventually pull the economy out of disequilibrium. Keynesians believe that fiscal policy—such as an increase in government expenditure or a reduction in taxation—is the most effective way to offset the lack of private demand.

A competing theory of income and employment, the monetarist approach, places the quantity of money in the controlling role. The analysis of the effects of increasing or decreasing the money supply is approximately parallel to that of the consumption-and-savings relation. The rules of thumb derived from the two theories may, in fact, be combined: an excess demand for goods or an excess supply of money (the two may be seen as aspects of the same phenomenon) will be associated with rising income; similarly, an excess supply of goods or an excess demand for money will be associated with falling income. Monetarists, such as Milton Friedman, have advocated monetary policy as the proper countercyclical tool of government.

Both the Keynesian and the monetarist theories have two notable shortcomings. First, both are demand-side theories and are therefore incapable of contributing toward the long-term considerations of economic growth. Second, both assume that people can be fooled over and over again; in reality, as they learn to anticipate government policies based on the monetarist or Keynesian models, people act in ways to offset these policies and thus negate the government actions.

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